Ordering Transitions in Short-Chain Alcohols
Alcohols present fascinating properties, both static and dynamic, to a large extent due to the presence of a hydrogen-bonded network. In the liquid state, hydrogen bonds (HB) are continuously forming and breaking on a timescale of 10–11 s at room temperat
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Abstract Alcohols present fascinating properties, both static and dynamic, to a large extent due to the presence of a hydrogen-bonded network. In the liquid state, hydrogen bonds (HB) are continuously forming and breaking on a timescale of 10–11 s at room temperature. Thus, these substances exhibit a rich dynamic behaviour at different time and length scales. Alcohols are considered complex systems in which structural and dynamic fluctuations in the HB network play a key role in the relaxation dynamics, as well as on the structural development. Revealing the interplay between the structural ordering and the relaxation dynamics during crystallization in short-chain alcohols is of paramount importance. One of the most powerful experimental methods to tackle this problem is dielectric spectroscopy (DS), not only because it offers information about characteristic time scales, but also because it allows obtaining information about the static properties of the system, at least in an indirect manner. In this chapter, we go through some of the most representative examples that illustrate the crystallization in short-chain alcohols by using dielectric spectroscopy, making special emphasis on those works in which dielectrics has been combined simultaneously with neutron diffraction (ND). This singular approach allows the crystal development to be tracked by means of ND, and the dynamic changes occurring in the disordered phase by DS, providing in this manner a complete picture of the structural ordering process. Keywords Crystallization · Neutron diffraction · Alcohols · Hydrogen-bonded liquids · Plastic crystals
A. Sanz (B) Glass and Time, IMFUFA, Department of Science and Environment, Roskilde University, P.O. Box 260, 4000 Roskilde, Denmark e-mail: [email protected] © Springer Nature Switzerland AG 2020 T. A. Ezquerra and A. Nogales (eds.), Crystallization as Studied by Broadband Dielectric Spectroscopy, Advances in Dielectrics, https://doi.org/10.1007/978-3-030-56186-4_4
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Abbreviations CNT DS Gcrys Gliq HB JMAK MW ND PC SCL Tg
Classical nucleation theory Dielectric spectroscopy Gibbs free energy of the crystalline state Gibbs free energy of the liquid state Hydrogen bond Johnson–Mehl–Avrami–Kolmogorov Maxwell–Wagner effect Neutron diffraction Plastic crystal Supercooled liquid Glass transition temperature
1 Introduction In this chapter, we will describe how dielectric spectroscopy techniques have contributed for a better understanding of the structure-dynamics correlations in low molecular weight alcohols. We will focus on the transformation of liquid short-chain alcohols into solid phases with periodic order, with especial attention paid to crystallization processes. Unlike liquids, where molecular entities exhibit rotational and translational mobility, in the true crystalline state, molecular motions are restricted to small oscillations about fixed positions in a regular lattice. According to thermodynamics, crystallization would be possible as soon as the difference between the Gibbs free ener
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